Open the mu-plugins/bp-blogs/bp-blogs-templatetags.php – Find this code starting at line 682 end at 696

<?php printf(__("By filling out the form below, you can <strong>add a blog to your account</strong>. There is no limit to the number of blogs you can have, so create to your heart's content, but blog responsibly.", 'buddypress'), $current_user->display_name) ?>

<?php _e("If you’re not going to use a great blog domain, leave it for a new user. Now have at it!", 'buddypress') ?>